Standard Model Higgs · 2005. 4. 27. · P. Sphicas/SSI2001 Studying EWSB at the LHC 3 SM Higgs (II) nDecays & discovery channels uHiggs couples to m f 2 lHeaviest available fermion

P. Sphicas/SSI2001

Standard Model HiggsStandard Model Higgs

Studying EWSB at the LHC 2P. Sphicas/SSI2001

SM Higgs (I)SM Higgs (I)n Production mechanisms & cross section


SM Higgs (II)SM Higgs (II)

n Decays & discovery channelsu Higgs couples to mf2

l Heaviest available fermion(b quark) always dominates

l Until WW, ZZ thresholds open

u Low mass: b quarks→ jets; resolution ~ 15%l Only chance is EM energy

(use γγ decay mode)u Once MH>2MZ, use this

l W decays to jets or lepton+neutrino (ETmiss)


Low mass Higgs (MLow mass Higgs (MHH


Intermediate mass HiggsIntermediate mass Higgsn H→ZZ→λ+λ– λ+λ– (λ =e,µ)

u Very cleanl Resolution: better than 1

GeV (around 100 GeV mass)u Valid for the mass range

130


High mass HiggsHigh mass Higgsn H→ZZ→ λ+λ– jet jet

u Need higher Branching fraction (also νν for the highest masses ~ 800 GeV/c2)

u At the limit of statistics


Higgs discovery prospects @ LHCHiggs discovery prospects @ LHCn The LHC can probe the entire set of “allowed” Higgs

mass values; u in most cases a few months at low luminosity are adequate for

a 5σ observation

CMS


Status of HStatus of H→→ bbbb ¯̄ (I)(I)n Low mass Higgs; useful for coupling measurement

u H→ bb̄ in t t ̄ H production

l σ.Br=300 fbl Backgrounds:

– Wjjjj, Wjjbb̄– t t ̄ jj

– Signal (combinatorics)

l Tagging the t quarks helps a lot

– Trigger: t →b(e/µ)ν– Reconstruct both t quarks

l In mass region90GeV


Status of HStatus of H→→ bbbb ¯̄ (II)(II)n H→ bb̄ in WH production

u Big background subtractionl Mainly: Wjj, t t ̄ (smaller: tX,WZ)

l Example (below) at 105:– in mass region88GeV


SM Higgs properties (I): massSM Higgs properties (I): massn Mass measurement

u Limited by absolute energy scalel leptons & photons: 0.1%

(with Z calibration)l Jets: 1%

u Resolutions:

l For γγ & 4λ ˜ 1.5 GeV/c2

l For bb ˜ 15 GeV/c2

u At large masses: decreasing precision due to large ΓH

u CMS ˜ ATLAS


SM Higgs properties (II): widthSM Higgs properties (II): widthn Width; limitation:

u Possible for MH>200l Using golden mode (4λ)

CMS


SM Higgs; width for MSM Higgs; width for MHH


SM Higgs properties (III)SM Higgs properties (III)n Biggest uncertainty(5-10%): Luminosity

u Relative couplings statistically limitedl Small overlap regions

Measure Error MH range→ γγ( )→( ) 30% 80–120

→ γγ( )→ ∗( ) 15% 125–155

σ( )σ ( ) 25% 80–130

→ ∗( )( )→ ∗( )( ) 30% 160–180


Strong bosonStrong boson--boson scatteringboson scatteringn Example: WLZL scattering

u W, Z polarization vector εµ satisfies: εµpµ=0; l for pµ=(E,0,0,p), εµ=1/MV(p,0,0,E) ≈ Pµ/MV+O(MV/E)

u Scattering amplitude ~ (p1/MW) (p2/MZ) (p3/MW) (p4/MZ), i.e. σ~s2/MW2MZ2

u Taking MH→∞ the H diagram goes to zero (~ 1/MH2)u Technicalities: diagrams are gauge invariant, can take out one

factor of sl but the second always remains (non-abelian group)

u Conclusion: to preserve unitarity, one must switch on the H at some massl Currently: MH≤700 GeV


The no Higgs case: VThe no Higgs case: VLLVVLL scatteringscatteringn Biggest background is Standard Model VV scattering

u Analyses are difficult and limited by statistics

L=300 fb-1

Resonant WZ scattering at 1.2 & 1.5 TeV Non-resonant W+W+ scattering

MH=1 TeV

WTWT


Other Other resonancesresonances/signatures/signaturesn Technicolor; many

possibilitiesu Example: ρT±→W±Z0

→λ±νλ+λ– (cleanest channel…)

u Many other signals (bb, t t resonances, etc…)u Wide range of

observability

ATLAS; 30 fb–1

––

P. Sphicas/SSI2001

SupersymmetrySupersymmetry

SUSY Higgses


Problems with the HiggsProblems with the Higgsn Quadratic divergence of its mass

u Λ is a cutoff momentumu Put simply: why is the Higgs mass low?

( ) ( ) ∫Λ

+Λ=


Supersymmetry Supersymmetry (SUSY)(SUSY)n One possible solution:

u for every particle there exists a partner particle with ½ spin difference

u With SUSY, infinities disappear:l As long as Mp=Msp


Supersymmetry Supersymmetry WorldWorldn SUSY doubles the

particle spectrumn It must also be

brokenu To explain why

unseen till nowu If broken at ESUSY:

( )( ) ∫+Λ

=


Supersymmetry Supersymmetry and Unificationand Unificationn Couplings “run” with Q2:

u Loop diagrams (quantum corrections) make the coupling between the force and matter particles dependent on the energy at which the interaction occurs

n Extrapolating the couplings for the EM, WK and strong interactions:

Without SUSY With SUSY


MSSM MSSM HiggsesHiggses: phenomenology: phenomenologyn Complex analysis; 5 Higgses (H±;H0,h0,A0)

u At tree level, all masses & couplings depend on only two parameters; tradition says take MA & tanβ

u Modifications to tree-level mainly from top loopsl Important ones; e.g. at tree-level, Mh1 TeV (i.e. no decays of the Higgses to them); well-studied

(b) M


MSSM MSSM HiggsesHiggses: masses: massesn Mass spectra for MSUSY>1TeV


MSSM: h/H productionMSSM: h/H productionn Biggest branch is tanβ


MSSM: h/A decayMSSM: h/A decayn h is light

u Decays to bb (90%) & ττ (8%)l Decays to cc, gg suppressed

n H/A “heavy”u Decays to top open (low tanβ)u Otherwise still to bb & ττu Negative: WW/ZZ channels

suppressed; lose golden modes for H

–

–

No mixing


Higgs channels consideredHiggs channels considered

n Channels currently being investigated:u H, h→γγ, bb̄ (H→bb̄ in WH, t t ̄ H)u h→γγ in WH, t t ̄ h → l γ γ

u h, H → ZZ*, ZZ → 4 lu h, H, A→ τ+τ− → (e/µ)+ + h− + ETmiss

→ e+ + µ− + ETmiss inclusively and in bb̄ HSUSY→ h+ + h− + ETmiss

u H+ → τ+ ν from t t ̄u H+ → τ+ ν and H+ → t b̄ for MH>Mtopu A → Zh with h →bb̄ ; A →γγ

u H, A → χ~02χ~~02, χ~0iχ~0j, χ~+iχ~−j

u H+ → χ~+2χ~02u qq →qqH with H →τ+τ− using OO code (tough…)u H →ττ, in WH, t t ̄ H work started; tough…

new and promising

(very) important and hopeful


MSSM MSSM HiggsesHiggses: last (published) results: last (published) resultsn Little room for h left; A is still “open”

– Maximal mixing:

• Mh>84 GeV/c2

• exclude 0.8


MSSM MSSM HiggsesHiggses: expected LEP reach: expected LEP reachn Taking 208 GeV and actual luminosity recorded

M(h)M(h)

tanβ

No mixingMax mixing

M(A)ta

nβ


H,AH,A→→ττττn Most promising modes for H,A

u τ’s identified either in hadronic or leptonic decaysu Mass reconstruction: takelepton/jet direction to be the τ direction


H, A reach via H, A reach via ττ decaysdecaysn Contours are 5σ; MSUSY=1 TeV


HH++ detectiondetectionn Associated top-H+ production:

u Use all-hadronic decays of the top (leave one “neutrino”)

u H decay looks like W decay →Jacobian peak for τ-missing ET

u In the process of creating full trigger path + ORCA analysis

ET(jet)>40

|η|


SUSY reach on SUSY reach on tantanββ--MMAA planeplanen Adding bb̄ on the τ modes can “close” the plane

Wh

bb̄(e/µ)ν

No stop mixing

maximal stop mixing with

30 fb-1 maximal stop mixingwith 300 fb-1


MSSM Higgs reach; MMSSM Higgs reach; MSUSYSUSY~1TeV~1TeVn Summary:

→ γγ

→ ∗( ) → l

→ ττ → (l/ ) + miss

, , → µµ; same for bb HSUSY

H ± → τ ±ν from t → Hbfrom H → tb

A → γγA → ZhH → hhA / H → tt


Observability Observability of MSSM of MSSM HiggsesHiggses

4 Higgs observable3 Higgs observable2 Higgs observable1 Higgs observable

MSSM Higgs bosons

h,A,H,H±

h,A,H,H±

Assuming decaysto SM particles only

h,H±

h

h,H±

h,A,H

H,H±

h,,H,H±

h,H

5σ contours


If SUSY If SUSY chargcharg(neutral)(neutral)inosinos < 1 < 1 TeV TeV (I)(I)n Decays H0→ χ~02χ~~02, χ~+iχ~-j become important

u Recall that χ~02→χ~~01l +l_ has

spectacular edge on the dilepton mass distribution u Example: χ~02χ~02. Four (!) leptons(isolated); plus two edges

Four-lepton mass

100 fb−1


If SUSY If SUSY chargcharg(neutral)(neutral)inosinos < 1 < 1 TeVTeV (II)(II)n Adding bb̄ on the τ modes can “close” the plane

Wh

bb̄(e/µ)ν

No stop mixing

maximal stopmixing with

30 fb-1 maximal stop mixingwith 300 fb-1

Area coveredby H0→ χ~02χ~~02,

→4l eptons100 fb-1


MSSM: Higgs summaryMSSM: Higgs summaryn At least one φ will be found in the entire MA-tanβ plane

u latter (almost) entirely covered by the various signatures, however:

u Full exploration requires 100 fb–1

u Difficult region: 3

P. Sphicas/SSI2001

SumersymmetrySumersymmetry

Sparticles


SUSY @ LHCSUSY @ LHCn Simplest SUSY

u Ample cross section for direct squark and gluino production

u Gauginos produced in their decay; example: qL→χ20qL

~ ~Msp(GeV) σ (pb) Evts/yr

500 100 106-107

1000 1 104-105

2000 0.01 102-103

M=500 GeV


SUSY mass scaleSUSY mass scalen Events with ≥ 4jets + ETmiss

u Clean: S/B~10 at high Meffu Establish SUSY scale (σ ≈ 20%)

Meff = PT, jj=1

4

∑ + ETmiss

LHCPoint 5

LHCPoint 1

SM

SUSY

Effective mass “tracks”SUSY scale well


SUSY decaysSUSY decaysn Squarks & gluinos produced together with high σ

u Gauginos produced in their decays; examples: l qL→χ20qL (SUGRA P5)l q → g q →χ20qq (GMSB G1a)

u Two “generic” options with χ0:(1) χ20→ χ10h (~ dominates if allowed)(2) χ20 → χ10λ+λ– or χ20 →λ+λ–

u Charginos more difficult l Decay has ν or light q jet

u Options:l Look for higgs (to bb)l Isolated (multi)-leptons

~

–

~ _~ ~

~


SUSYSUSYn Huge number of theoretical models

u Very complex analysis; MSSM-124u Very hard work to study particular scenario

l assuming it is available in an event generatoru To reduce complexity we have to choose some “reasonable”,

“typical” models; use a theory of dynamical SYSY breakingl mSUGRAl GMSBl AMSB (in less detail)

u Model determines full phenomenology (masses, decays, signals)


SUGRASUGRAn Five parameters

u All scalar masses same (m0) at GUT scaleu All gaugino masses same (m1/2) at GUT scaleu tanβ and sign(µ)u All tri-linear Higgs-sfermion-sfermion couplings common value

A0 (at GUT scale)

n Full “particle table” predictableu 26 RGE’s solved iterativelyu Branches: R parity (non)conservationu Extensions: relax GUT assumptions (add parameters)


mSUGRAmSUGRAn Simplest SUSY

u Ample cross section for squarkand gluino production

u Gauginos produced in their decay; example: qL→χ20qL

~~


SUGRA spectroscopySUGRA spectroscopyn Basic assumption: mass universality

u Scalar masses: m0; u gaugino masses: m1/2; u Higgs masses: (m02+µ2)1/2

n RGE: run masses downto EWK scale

u M(squark): large Increase (due to α3)u M(slepton): small increase(due to α1, α2)u Gauginos: gluino is fast-rising; B-ino, W-ino mass decreasesu Mixing leads to charginos (2) and neutralinos (4)

n Higgs: strong top coupling drives µ2


Sparticles Sparticles in SUGRAin SUGRAn Contours of fixed g/q and χ/λ mass~ ~ ~

~

22/1

20

2/1

6)~(

3)~(

mmqm

mgm

+≈

≈2

2/120

2/1022/1

01

)15.0,5.0()~,~(

;)~,~( ;2/)~(

mmm

mmmm

RL +≈

≈≈±±

±

λλ

χχχ


SUGRA: the five LHC pointsSUGRA: the five LHC pointsn Defined by LHCC in 1996

u Points 1,3,5: light Higgses l LEP-excluded (3; less for 1,5)l Restore with larger tanβ

u Points 1&2:l Squark/gluinos ˜ 1TeV

u Point 4: at limit of SBl Small µ2, large χ,φ mixing l Heavy squarks

u Point 5: cosmology-motivatedl Small m0→light sleptons

→ increase annihilation of χ10

→ reduce CDM

P M0 M1/2 A0 tanβ s(µ)

1 400 400 0 2 +

2 400 400 0 10 +

3 200 100 0 2 –

4 800 200 0 10 +

5 100 300 300 2.1 +


SparticlesSparticles (e.g. SUGRA)(e.g. SUGRA)n Formidable number of options

u Five parametersl All scalar masses same (m0) at GUT scalel All gaugino masses same (m1/2) at GUT scalel tanβ and sign(µ)l All tri-linear Higgs-sfermion-sfermion couplings common

value A0 (at GUT scale)

n Full “particle table” predictableu 26 RGE’s solved iterativelyu Branches: R parity (non)conservationu Extensions: relax GUT assumptions (add parameters)


Experimentally: spectacular signaturesExperimentally: spectacular signaturesn “Prototype”: χ20 → χ10λ+λ–

u Straightforward: dileptons + ETmiss

u Example from P3l SM even smaller with b’sl Also works at other pointsl But additional SM (e.g. Z0)

u ∆M measurement easyl Position of edge; accurate

~ ~


Dileptons Dileptons @ other points@ other pointsn Multi-observations

u Main peak from χ20→χ10λ+λ–

l Measure ∆m as beforeu Also peak from Z0 through

χ20→χ10Z0

l Due to heavier gauginos l P4 at “edge” of SB → small µ2 →(a) χ± and χ0 are light(b) strong mixing between

gauginos and Higgsinos

u At P4 large Branching fractions to Z decays:l e.g. B(χ3→χ1.2Z0)˜ 1/3; size of peak/PT(Z)→info on masses

and mixing of heavier gauginos (model-dependent)

LHCPoint 4

~

~

~

~

~

~ ~


Determining SUSY parametersDetermining SUSY parametersn From the edges of the spectra

u @ P5: qL→qχ20→qλλ→qλ+λ–

u ATLAS example:l 2 isol, OS leptons+=4jets+ETmiss

l Combine leptons with 2 harder jets

l Similarly, minimum at 270 GeV/c2

l Both min & max visiblel Example shown: eµ subtracted

~

( )( )550

2/1

2

2222~

max

02

01

02

02 ≈

−−=

χ

χχχ

M

MMMMM L

q

qλλ

~ ~


Distinguishing 2 & 3Distinguishing 2 & 3--body decaysbody decaysn Two scenarios can be disentangled directly

u From asymmetry of twoleptons:

u In analogy with τ decays

minT

maxT

minT

maxT

PPPPA

+−=


SUGRA reachSUGRA reachn Example from Point 1

u tanβ=2;A0=0;sign(µ)=–u But look at entire m0-m1/2

planeu Example signature:

l N (isolated) leptons + = 2 jets + ETmiss

l 5σ (σ=significance) contours

u Essentially reach is ~2 (1) TeV/c2 for the m0(m1/2) plane

CMS100 fb–1


The other scenario: The other scenario: χχ2200→→ χχ1100hhn Followed by h→bb: h discovery at LHC

u E.g. at Point 1, ≈20% of SUSY events have h→bbl But squarks/gluinos heavy (low cross sections)

u b-jets are hard and central

–

u Expect large peak in (b-tagged) di-jet mass distribution

u Resolution driven by jet energy measurement

u Largest background is other SUSY events!

–


Building on the hBuilding on the hn In analogy with adding jets to χ20 →χ10λ+λ–

u Select mass window (e.g. 50 GeV) around hu Combine with two highest ET jets; plot shows min. massu Again, use kinematic limits

l Case shown: max ˜ 550 GeV/c2

u Beyond this:l Model dependence ATLAS

30fb–1


Observability Observability of decays into hof decays into hn Examples from CMS (tanβ=2&10)


Varying Varying tantanββn τ modes eventually become important

u At tanβ>>1 only 2-body χ20 decays (may be): χ20→τ1τ→ ττχ10

n Visible eµ excess over SM; for dilepton edge: need ττ mass

~~ ~ ~


SUSY parameters; SUGRASUSY parameters; SUGRA

ok2.00±0.08400±8400±100P1 @100fb-1

ok10±2400±8400±100P2 @100fb-1

ok10±2200±2800±50P4 @100fb-1

ok±0.1300±3100±4P5 @10fb-1

s(µ)tanβm1/2 (TeV)m0 (GeV)Point/Lumi

Essentially no information on A0(Aheavy evolve to fixed point independent A0)

Documents

Standard Model Higgs · 2005. 4. 27. · P. Sphicas/SSI2001 Studying EWSB at the LHC 3 SM Higgs (II) nDecays & discovery channels uHiggs couples to m f 2 lHeaviest available fermion